Various solutions to the aforementioned problem have been proposed to date. For example, U.S. Pat. No. 5,441,344 illustrates a pan on which the measurement and display of the temperature is obtained by a sensor, e.g. a thermocouple, in direct thermal contact with the cooking surface or by means of a clip applied to the side wall of the pan. An electronic circuit, connected to the sensor, measures and displays the temperature on a display located in the handle or on the clip.
Similarly, EP 0950368 illustrates a pan containing a temperature sensor consisting of a resistant track applied on a layer of insulating material that covers part of the surface of the pan. The resistant track has a variable temperature coefficient with the ends connected to a circuit for the measurement of the resistance or variation of the resistance, which it converts into the temperature value.
Further, EP 0931495 illustrates a pan having a temperature probe inserted in the bottom and connected to an electronic circuit for the measurement and display of the temperature. The probe and the conductors connected to the electronic circuit extend between the section making up the bottom of the pan and a perforated plaque fastened by cold molding technology to this section.
EP 0931496 illustrates a different solution consisting of a pan equipped with an infrared sensor located on the handle and connected to an electronic circuit for the transformation of the infrared rays into an electrical signal.
The solutions listed above are complex and expensive to apply, requiring alterations in the structure of the cooking utensil and/or the use of electronic circuits.
A device that makes no use of electronic circuits is illustrated in EP 0901005. The device is designed to indicate the temperature of vessels containing a food product to be heated and comprises a mixture of liquid crystals that change color between 35° C. and 45° C., causing a single message to appear in letters on a background having the same color of the mixture prior to changing color.
The device illustrated in EP 0901005 is useful for vessels, such as infants' nursing bottles, which need only to be heated slightly (35-45° C.) and where only a single message has to be displayed within a determined limited temperature range, while it is unsuitable for cooking utensils designed to operate at much higher temperatures (100-265° C.) and where more information and a broader temperature range are desirable.
A handle for cooking utensils according to the preamble of claim 1 is known from FR 2,521,867. This document discloses a handle for cooking utensils make of a material with low heat conductivity and comprising an plate in a material with a high thermal conductivity with one end in thermal contact with the body of the utensil and the other end at a distance from it, and thermo chromatic means applied on the plate; these latter having the ability to change color within specific ranges of temperature so as to display information, related to the temperature of the bottom of the utensil, in different areas of the plate.